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Mps Affecting Chlorine Results?


BlueSpa

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I'm sure this has come up before but I've been unsuccessful in finding it thru the "search" so thought I'd post.

I've usually been adding a small amount (about 0.5oz or less) of MPS after soaking and monitoring the Chlorine levels with the Taylor kit. Usually shock once a week with about 2oz of MPS and enough Dichlor to get at least 5ppm FC, then just monitor the FC levels to be sure we have about 2ppm (also have ozonator, water volume 750gal).

Yesterday our FC level was 2.4ppm (Taylor K-2006 kit) and the CC was 0. Last night I added 1oz of MPS after soaking and this afternoon when I tested the water with the Taylor kit it showed 3.4ppm FC, 0.2ppm CC. In reading the Taylor booklet it does mention that MPS can affect the CC readings but am wondering why the FC levels are elevated when no Cl was added?? I do have the test kit in an area that's about 55 degrees so the reagents are cool when I'm doing the test but this appeared to be within the Taylor working temps and it's been that way for all my readings for the past month or so.

Should I get that other Taylor reagent they mention for pool folks that shock with MPS if I'm going to be using both the MPS and Cl in my spa?? (sorry I forgot the name and the booklet isn't handy)

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Very soon after adding MPS it can register not only as CC but also as FC. The reason is that the non-chlorine shock you purchase is not pure. It not only contains the triple salt of K2SO4•KHSO4•2KHSO5, but has additional impurities including about 3% potassium peroxydisulfate (persulfate), K2S2O8, and it is this substance that is a very strong oxidizer that shows up as FC. However, it tends to break down rather quickly, especially in spas that use N2 since silver ion catalyzes its breakdown. The remaining monopersulfate (MPS), HSO5-, is what generally registers as CC, but may register as FC if it's high in concentration.

Some people on this forum have tried using the MPS interference remover from Taylor (shown here) with mixed success. You could try it, but it doesn't seem to be a sure thing.

Richard

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Thanks Richard. I'm actually testing about 24 hours after adding the MPS but may try the Taylor interference remover kit. (Last night we added 0.5oz of MPS after soaking and upon testing tonight the FC was back at 2.4ppm, CC is 0.) Maybe I'll go back to adding Cl after a soak and save the MPS for weekly shocking, which is what we originally did and seemed to work ok.

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Hi,

Here's a test you can perform to determine MPS compound as chlorine.

I can't remember if I copied from this forum or the Taylor website.

jeff

Monopersulfate Compound Test

1. Rinse and fill sample tube to 25 mL mark with water to

be tested.

2. Add 1 heaping dipper R-0870. Swirl until dissolved.

3. Add 10 drops R-0003. Swirl to mix. WAIT 1 MINUTE.

4. Add R-0871 dropwise, swirling and counting after each

drop, until color changes from pink to colorless.

5. Multiply drops of R-0871 by 0.2. Record as ppm total

oxidizer (TO).

6. To calculate ppm monopersulfate compound (MC) as chlorine:

MC = TO - (FC + CC). Record as ppm.

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The Taylor MPS interference remover I referred to in my post is in kit K-2041 and the instructions are here. However, not everyone who has used this has had good results.

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Here's a test you can perform to determine MPS compound as chlorine.

-snip-

5. Multiply drops of R-0871 by 0.2. Record as ppm total

oxidizer (TO).

6. To calculate ppm monopersulfate compound (MC) as chlorine:

MC = TO - (FC + CC). Record as ppm.

Thanks Jeff. I ran this test today. I added some dichlor on Thursday night after soaking, no MPS since Wednesday night, so I was curious if the test would indicate any MPS present.

Here are the results but I could use some expert help with the interpretation -

TO = 3.2 ppm Total Oxidizer

FC = 2.8 ppm Free Chlorine

CC = 0 ppm Combined Chlorine

MC = 0.4 ppm MPS Compound as Chlorine

My confusion is with the "as Chlorine" part of the MPS as Chlorine test. This test is quantifying the amount of MPS that the routine test is showing as FC, so 0.4ppm of my FC result is actually MPS, even though the TO (total oxidizer) result indicated 3.2ppm of total oxidizer??

I'll add some more MPS tonight after we soak and see what the results are tomorrow too.

I had sent an inquiry to Taylor the other day asking about the interference and the 2041 kit but they haven't gotten back to me yet. Will post if/when I hear something.

Thanks for everyone's help - this forum is certainly helpful!!!

Barb

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Hi Barb,

I agree with your interpretation of FC actually being 2.4ppm though I don't have the background like chemgeek to explain it fullly.

I have had my tub about 6 months now and change water monthly (small tub, lotsa use). The first 6-8 weeks I probably performed 100 tests on my water. Today I don't fret the results too much. I make sure there's ample FC and keep the pH balanced.

enjoy.

jeff

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